The conventional front suspension system used by bus manufacturers is generally of the independent type, such that shocks and vibrations received by one wheel are not transmitted to the other wheel. The suspension system consists of a frame type mechanism with four articulated bars or links having a main rubber torque spring with a circular cross-section that forms one of the lower joints of the four bar mechanism.
For the purpose of illustrating the conventional suspension system, which is the object of the improvements of the new front suspension of the present invention, a conventional spring assembly is illustrated in FIGS. 1-4. FIGS. 1-4 are referred in a general way for the description of the background of the invention. FIG. 1 schematically shows the arrangement of the independent suspension having four articulated bars shown on each side of the suspension. As can be seen, the left side is symmetrical with the right. The frame or chassis of the vehicle is supported on bars 2 and 4 by means of the joints A and D, while the bar 3 is supported on bars 2 and 4 by means of joints B and C. Bar 3 is joined to the steering yoke where the wheel is mounted. In this suspension system, the joint D is constituted by the torque spring which supports the load of the bus.
FIGS. 2A and 2B illustrate the suspension of the prior art comprising the torque spring of the suspension that acts as a large dimension bushing that absorbs the vibration and noise of the wheels, preventing the vibrations from reaching the body to provide the bus with a comfortable ride. The conventional torque spring assembly 5 is formed by a cylindrical, molded rubber body 6 vulcanized on a steel pipe 7. Steel sheet casings 8 are mounted on the exterior of the rubber body 6, as shown in FIG. 2A. To carry out the spring functions, the spring is pressure inserted into a pipe 9 having an arm 15 welded thereon for mounting the spring assembly to the suspension system of the vehicle. The spring assembly 5 is previously torqued such that it is able to support the loads submitted by the weight of the bus. An adjustment lever 10 is welded at each end of the steel pipe 7 prior to assembling into the pipe for adjusting the torque of the spring. FIG. 2B illustrates the spring assembly 5 in the assembled condition. The tension of the spring and arm assembly supporting the loads of the bus suspension traveling on the highways can thus be set. The ends of the pipe 7 of the spring and arm assembly are fixed to the frame with two supports that constitute the points where the frame is supported on the suspension.
It is an inherent characteristic of the rubber torque spring that with use it relaxes, such that the load capacity of the spring is partially lost, and the height of the bus with respect to the ground is reduced. When this happens, it becomes necessary to retighten the spring, by adjusting the position of adjustment levers 10 with respect to the chassis as indicated in FIG. 4.
The torque spring is designed to have a long useful life. However, it becomes necessary to replace the spring when it is impossible to retighten the spring, due to the great number of kilometers the bus travels during service.
A disadvantage of the prior art circular section torque spring is that to tighten this rubber spring body 6, the adjustment levers 10 must be removed and again welded on the shaft in another angular position. The welding typically burns the rubber of the spring thereby reducing the life of the spring. Further, to effect this operation, it is necessary to remove the spring and arm assembly from the bus.
Another disadvantage of the prior art spring and arm assembly of the conventional suspension is that when a spring's useful life has ended and must be replaced, special equipment is required to pull or push the rubber spring body under pressure from inside the pipe. This involves the need for a specialized machine shop to change the springs, resulting in considerable time and expense for maintenance.
To support the suspension assembly made up of the spring and arm in the wheels, there are four elements that allow the movement of each wheel independently and support the bus. One of these elements is a yoke 11 that together with the arm welded to the torsion spring pipe, form the link or bar 2 of the articulated four bar mechanism represented in FIG. 3. The yoke 11 is mounted on the arm 15 of the spring assembly via a welded conical trunnion 12 having a threaded end. The yoke includes a conical hole that is assembled on the trunnion and is fastened to the trunnion by means of a washer and nut. The yoke also includes a pair of bushings with different interior diameters for receiving a tapered bolt forming part of joint C.
Another support element of the spring and arm assembly consists in a vertical Joint arm, which in the diagram of FIGS. 1 and 3 constitutes bar 3, which serves to connect the bars 2 and 4 and to join the steering yoke.
The joint C constitutes the zone of greatest load and wear on the front suspension and therefore requires periodic lubrication. The Joint C is formed by a bolt with two different diameters on its ends and a conical middle section to firmly unite the bolt with a conical hole in the joint arm. The tightening of the bolt with respect to the bolt is done with a special thin nut that is arranged on one side of the joint arm in the middle part of the yoke. The relative movement of the elements occurs between the bolt and the yoke, which has a pair of bushings. The joint is typically lubricated by means of grease cups installed on both sides of the yoke so that the grease passes through a hole in the bolt of the joint and through transverse holes in such bolt, which empty into the space between the bushings and the contacting surfaces of the bolt.
The above-described assembly and lubrication system has the inconvenience of requiring special tools for tightening the bolt and for later disassembly to change bushings, since it is necessary to remove the bolt to access the bushings. The bolt extraction operation involves applying a load with an extractor on the end of the bolt and alternately loosening the thin nut provided in the middle of the yoke. The lubrication for this type of assembly tends to be deficient because a large part of the grease escapes through an end of the bolt while it is injected in the other end, and therefore in some cases the bushings remain unlubricated, resulting in premature wear of the bushings. The worn bushings which are not replaced can cause abnormal wear of the tires due to the loss of alignment caused by the excessive play between the bolt and the yoke bushings.
The conventional suspension system also has an upper control arm that through the joint A serves as a support for the body of the vehicle. The control arm is joined with the arm Joint at the point defined by joint A or joint B, where the elements of the front suspension are located in order to adjust the slope of the wheel.
Joint A of FIG. 1 is formed by two bolts that are fixed to two supports by means of screws that pass through a groove formed in the supports and a half-moon type chock. On each of these bolts are mounted two conical bushings opposing each other. Between the bushings is located one of the two parts that form the upper control arm in joint A. The ends of the bushing having opposing conical surfaces allow assembling of the bushings by means of a washer and a grooved cotter nut.
Joint A described above has the inconvenience of excessive wear in the bushings when correct alignment of the front wheels is not maintained, mainly due to the effect of an improper caster. When there is high wear of these bushings, there is also wear on the inner portion of the tires, which is quickly increased due to the loss of correct angle of the tire as a result of the excessive play between the bushings and the bolts.
Another characteristic of the front suspension presently in use is that it has two shock absorbers, one for each spring, whose main function is to control the movements of the wheel. The shock absorbers allow only a certain number of vertical movements that are diminished by the action of the shock absorber and controls the speed and number of lateral movements of the bus. Due to the increased height of the bus, a common report is the presence of excessive lateral and longitudinal movements that make control of the vehicle difficult on mountainous roads, attributed to deficiency of the shock absorber system.
Since the conventional rubber torque spring by itself does not have the sufficient capacity to support the load of the bus and of the people and baggage it transports, the known suspension system has to be complemented with an auxiliary suspension of air chambers and a pneumatic system for air feed and control of such chambers. The pneumatic system increases the weight which must be supported by the suspension system.
Even when the round section rubber torque spring suspension provides a comfortable and safe suspension system, problems in regard to fast, easy, lasting maintenance and load capacity of the system typically occur.